This invention relates to a portable, power operated post driving apparatus that can be operated by a single person to drive a steel fence post, or other kinds of posts, into the ground in an expeditious manner.
Posts, particularly steel fence posts, have been driven into the ground in a number of different ways.
Originally, such posts were manually driven into the ground by using a sledge hammer. Other manually operated post drivers are described in U.S. Pat. Nos. 3,712,389 and 5,020,605.
Power driven post drivers of various sorts appear in the prior art. Examples include cam driven post drivers where an electric powered cam drives the hammer directly (U.S. Pat. No. 2,703,479) or where an electric or gas powered cam lifts the hammer and drops it (U.S. Pat. No. 4,984,640).
Various other power driven post drivers have been suggested by the prior art. These drivers use either compressed air or hydraulics to operate a fluid operated power cylinder arrangement wherein a weight assembly is lifted and lowered. One such device is described in U.S. Pat. No. 4,665,994 wherein the weight assembly comprises a metal disc and two solid metal bars. Such devices, although technically portable, are still very heavy because the combination of the weight of the weight assembly and the weight of the remainder of the apparatus. Such pneumatic post drivers use large amounts of compressed air, typically from 25 cubic feet per minute up to 125 cubic feet per minute. Such drivers require a relatively large air compressor to supply compressed air to the driver.
U.S. Pat. No. 5,819,857, issued to the inventor of the present apparatus, describes a vastly improved portable power driven post driver. The entire contents of U.S. Pat. No. 5,819,857 are hereby incorporated by reference.
The post driver of the '857 patent has an inner hollow cylinder open at both ends and adapted to receive a post through a lock clamp located at its lower end. An outer hollow cylinder having a closed upper end, and slightly larger in diameter than the inner cylinder, is located in sliding engagement over the inner cylinder. First and second power cylinders are attached to upper and lower surfaces of the outer cylinder in alignment with each other. A common piston rod connects the pistons of the power cylinders. A stationary fastening pin extends through a slot in the wall of the outer cylinder and is attached to the wall of the inner cylinder. A valve and conduit means communicate the two power cylinders to a source of fluid under pressure.
During operation of the post driver of the '857 patent, a post is inserted through the lock clamp in the lower end of the inner cylinder until it abuts the closed upper end of the outer cylinder and is locked in place. The valve alternately communicates the fluid under pressure with the first and second power cylinders to alternately raise the outer cylinder above the inner cylinder and then to drive the outer cylinder downward until the closed end thereof forcefully contacts the upper end of the post. The outer cylinder has handle means attached thereto to permit an operator to carry and hold the driver during operation. The post driver is thus configured to cause all of the weight of the driver, except for the weight of the inner cylinder, to drivingly engage a post to be driven.
The valve employed in the post driver of the '857 patent is a four way spool valve, such as Model No. 422CS011K manufactured by Parker. It has been found that although this valve functions to properly operate the post driver, it is expensive and difficult to perform maintenance thereon.